1 Modeling of Common Terns, Sterna hirundo, on Lake Champlain and Predictions for the Future

2 The Common Tern, Sterna hirundo, is a small, migratory water bird whose extensive range includes nesting islands on Lake Champlain. The history of Common Terns in Vermont includes population declines from hunting and predation, leading to their addition to the state’s Endangered Species List in 1989. Since then, they have been managed intensively such that their population in Vermont has made a comeback, rising close to the threshold for downlisting to threatened: 200 breeding pairs with a reproductive rate of 0.6 fledglings per pair. This thesis analyzed past data to project the tern population size into the future to assess whether the Common Tern should be down listed. My model showed that while the population can maintain an average of 200 breeding pairs over 50 years, it was unable to reach 0.6 fledglings per pair rate, a second requirement for down listing. The model also evaluated the effect of high water events-which decrease chick survival- on the tern population’s probability to reach the recovery goals. An increase in the probability of a high water event above the current rate of 0.38 yielded a tern population that could not reach either of the recovery criteria. Without reaching a rate o